The requirement would come as part of the administration’s phased approach to easing travel restrictions for foreign citizens to the country. No timeline has yet been determined, as interagency working groups study how and when to safely move toward resuming normal travel. Eventually all foreign citizens entering the country, with some limited exceptions, are expected to need to be vaccinated against COVID-19 to enter the U.S.

The official spoke on the condition of anonymity to preview the policy under development.

The Biden administration has kept in place travel restrictions that have severely curtailed international trips to the U.S., citing the spread of the delta variant of the virus. Under the rules, non-U.S. residents who have been to China, the European Schengen area, the United Kingdom, Ireland, Brazil, South Africa and India in the prior 14 days are prohibited from entering the U.S.

All travelers to the U.S., regardless of vaccination status, are required to show proof of a negative COVID-19 test taken within three days of air travel to the country.

The Biden administration has faced pressure to lift some restrictions from affected allies, the air travel industry and families who have been kept separated from loved ones by the rules. Many have complained that the travel restrictions don’t reflect the current virus situation—particularly as caseloads in the U.S. are worse than in many of the prohibited nations.

Airlines for America, a trade group for major U.S. airlines, said it was pleased by reports that the administration plans to make it easier for more foreign travelers to enter the country if they have been vaccinated.